A variety of compact sorting machines exist for receiving and sorting sheets from an output slot of a paper sheet processing machine, such as a machine. Generally, these sorting machines provide a number of trays supported in a compact vertical stack, each of which, in turn, is capable of traversing past the sheet output slot. To accommodate paper entry into each receiving tray in turn, a relatively large gap is required between the receiving tray and the tray immediately above the receiving tray. Tray spacing elsewhere may be minimized in order to increase the compactness of the vertical stack. Several tray shifting methods have been devised to accomplish this variable tray spacing requirement.
One sheet sorting machine, taught in U.S. Pat. No. 4,343,463, issued to Lawrence on Aug. 10, 1982, uses two rotating spiral cams to shift each tray, in turn, past the output slot of a copy machine. One drawback to this device is that spring means are needed to force two protruding trunnions of the next tray to be shifted into the cam tracks of the rotating spiral cams. This spring tension must be overcome when the trays are returning from the opposite direction. Moreover, relatively complex tray support frames are needed to ensure that each tray is properly positioned as the tray is to be moved by the rotating cams. Another drawback to this tray shifting technique is that the tray support frame must be allowed to move with the bottom tray, adding to the complexity of the machine. Other sorting machines also utilize this tray shifting means.
Another tray shifting method utilizes two rotating wheels, each with two or more notches formed in their perimeters. Upon rotation of each wheel, one notch engages a trunnion on either side of the next tray to be shifted and transports it along a track otherwise blocked by the wheel. Similar drawbacks exist for this type of tray shifting method, as spring biasing means must be employed to ensure that the trunnions of the next tray to be shifted will properly engage each notch in each wheel. Moreover, as the wheels engage the trunnions of a tray, a sudden strain is introduced to the rotational driving means of the wheels by the weight of the tray, which is often considerable when the tray is supporting a large number of sheets. As a result, driving force and support structure requirements are significant.
The prior art teaches, in moving bin sorting machines, that all trays, as an assembly, and in some cases a retaining frame as well, must be lifted by a single pair of trunnions, one on each side of the assembly. This results in excessive wear and a low mean time between failure.
Clearly, then, there is a need for a simple, reliable method of shifting trays sequentially past an output slot of a copy machine while providing a larger distance between the receiving tray and the tray immediately above the receiving tray, and a smaller distance between each of the other adjacent trays. The present invention fulfills these needs and provides further related advantages.